Mail problems - contacts "hacked"

Hi,

Forgive my ignorance, however, I have had a brief scan through these pages and several people appear to be having almost the same problem as I am, but not quite. I have an iphone 4 on iOS5.1, an ipad on iOS5.1.1, and a MacBook Pro, on OSX10.6.8.

This morning, at 0610 hours, GMT, my entire mailing list was sent a forwarded e-mail - junk of course, about bankruptcy, saying "Look here!" - which I did not send, and which does NOT show up in my Sent folder. However, I keep a bogus email address at the top of my list, so I get MailerDaemon failure messages, if such a thing occurs (a holdover, from when I used Windows).

My problem is, I have not used my MacBook in weeks, using only the iPad and iPhone. About a month ago, I received a similar e-mail from a family member, who also uses an iPad, which I didn't open but deleted, using my iPad.

Is it possible for any such botnet/Trojan/"virus" to have "infected" or nicked my mailing list, and, if so, how do I get rid of it? I have an elderly relative, who has an iPad2, and he opened the email (though not the extension), this morning, so he is now in a panic that he is next!

My e-mail account is through BTYahoo, but, as they have accessed EVERY one of my contacts, it appears likely that this has come from within, rather than without.

Can any of you advise or assist?

I have installed the trial of MacScan, this morning, following recommendation on another page here, and am running it as I type.

If anyone can help, I would be most grateful.

Kind regards,

Scoots.

PS, I recall now I DID notice that, yesterday afternoon, my iPhone burned its way through around 60% of the battery life, while I was using Kindle, in around 3 to 4 hours. I put it down to a glitch, or having left apps running in the background...obviously not.